Who could be the main antagonist in a 'Harry Potter x Alice Cullen fanfic'?

It could be a new dark wizard who has somehow tapped into the power of both the wizarding world and the Narnian magic in a negative way. This wizard might want to rule both realms and is using dark magic from both to achieve his goals.

A jealous student could be the main antagonist. This student might have a crush on Alice and see Bella as a threat to their relationship. They could start spreading rumors about Bella, trying to make her look bad in front of Alice and the other students.

A powerful dark wizard who has infiltrated the Troll Market and is using it as a base to gather dark magic items. He could be after the Elder Wand or some other powerful artifact from the Harry Potter universe and is using the chaos and secrecy of the Troll Market to his advantage. He would see Harry Potter as a threat to his plans and try to eliminate him.

Another option could be a corrupted version of Asriel. Maybe Alice's arrival somehow stirs up the darker parts of his past and he becomes a force against her, believing she is a threat to the delicate balance in the Underground.

Maybe a powerful and ancient being that has been awakened by the mixing of the two magical worlds of Harry Potter and Twilight. This being is enraged by the existence of both wizards and vampires and wants to wipe them out. Harry and Rosalie, being representatives of their respective groups, must join forces to stop this ancient and powerful foe. Their combined skills and the unique powers of their friends from both worlds would be crucial in this fight.

The main antagonist could be a powerful necromancer who combines the dark arts of Skyrim with some elements of Voldemort - like magic. He could be raising an army of the undead and causing chaos across Skyrim, which Harry has to stop.

It could be a new dark wizard who has a vendetta against Harry. This wizard might use a spell to stop Harry from eating, thinking it will weaken him before a final showdown. He could be someone who was once a follower of Voldemort and now wants to take his place and prove himself by getting rid of Harry.

Maybe an ancient evil spirit that was once bound but is now trying to break free by using the summoner as a conduit. This spirit could be manipulating events from the shadows, causing chaos in the wizarding world to draw the summoner out.

One idea could be that Harry discovers a hidden portal that leads him to the Twilight world where he meets Alice Cullen. They then team up to fight a new dark force that is threatening both their worlds.

Friendship and alliance is another big theme. Since they come from different worlds, the idea of how Harry and Alice (or other characters from their respective worlds) can become friends or allies is explored. This often involves overcoming prejudices. For instance, wizards might be wary of vampires at first, but then find common ground.